1. Field of the Invention
The present invention relates to a laser scanning unit and an image forming apparatus having the same.
2. Description of Related Art
An image forming apparatus that forms an image on a recording paper in an electrophotographic process (printer, facsimile apparatus, copier, multifunction apparatus, and the like) is provided with a laser scanning unit, in which a light deflector deflects a light beam emitted from a light source so as to scan a photoconductor for forming a latent image thereon. In order to maintain at a constant level, the light intensity of the light source, which fluctuates according to environmental change, such as a temperature change and the like, the laser scanning unit performs light intensity control, in which the unit detects an actual light intensity of the light source so as to control a driving current of the light source. Further, in order to properly expose a predetermined image forming area on the photoconductor, the laser scanning unit performs synchronization control, in which the unit detects a returning beam so as to control a scan timing, the returning beam being the light beam emitted from the light source and then reflected and returned by a mirror.
Such a laser scanning unit is generally provided with separate light detecting sensors: a sensor for detecting the light intensity of the light source for light intensity control; and a sensor for detecting the light beam for synchronization control. In order to reduce cost by reducing the number of parts, however, technology is known in which a light detecting sensor provided proximate to a light source is used for detecting both the light intensity of the light source and a light beam for synchronized control; a mirror reflects and returns, to an emitting position, the light beam for synchronization control emitted from the light source; and thereby the light detecting sensor provided proximate to the light source performs detection (Refer to Related Art 1).
[Related Art 1] Japanese Patent Laid-open Publication H3-245115 (FIGS. 1 and 3)
Misalignment of a light beam path due to optical axis misalignment stemming from a forming error is inevitable in an f-θ lens, which is provided to allow the light beam to form an image on the photoconductor. In the aforementioned conventional art, when the synchronization mirror reflects and returns, to the emitting position, the light beam for synchronization control emitted from the light source, the light beam passes through the f-θ lens twice in total: on an outgoing path from the light source to the synchronization mirror, and on a returning path from the synchronization mirror to the emitting position. The f-θ lens thus has a huge impact to the light beam for synchronization control. When the light beam returning to the emitting position largely deviates from a proper position, a problem occurs where the detection accuracy of the light beam declines.
Further, misalignment of the light beam path due to commonly-called axis inclination is inevitable in a light deflector having a rotating polygon mirror. The axis inclination is a phenomenon where a rotating axis deviates from a proper position during rotation. In the aforementioned conventional art, when the synchronization mirror reflects and returns, to the emitting position, the light beam for synchronization control emitted from the light source, the light beam is reflected by the light deflector twice in total: on the outgoing path from the light source to the synchronization mirror, and on the returning path from the synchronization mirror to the emitting position. The light deflector thus has a huge impact to the light beam for synchronization control. When the light beam returning to the emitting position largely deviates from a proper position, a problem occurs where the detection accuracy of the light beam declines.